1
ME 201
Thermodynamics
First Law for Closed Systems Guide
Recall that for a closed system there are no mass inflows or mass outflows, so the
mass of the closed system remains constant throughout the process or
m
=
m
1
2
Also, due to our quasistatic equilibrium assumption, we can not have any shaft work
out of a closed system. We can rewrite our 1st law equation as
W

W

Q
=
)
e

m(e
bnd
sh
1
2
For most closed systems we can neglect kinetic energy and potential energy changes.
We call these simple closed systems and can write our energy conservation as
W

W

Q
=
)
u

m(u
bnd
sh
1
2
Some examples of simple closed systems include
PistonCylinder System
Rigid Tank or Container
Balloon
In solving simple closed system problems, we need to identify the unknowns, so we
will know how to proceed. The possible unknowns are
Heat Transfer
Shaft Work
Boundary Work
Initial State (State 1)
Final State (State 2)
We first observe that heat transfer and shaft work can only be calculated from the first
law. This means only one of them can be unknown. If shaft work is not explicitly
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '06
 SOMERTON
 Thermodynamics, Entropy, final state

Click to edit the document details